Measurement of associated Z + charm production in proton-proton collisions at $\sqrt{s}=$ 8 TeV

Abstract

A study of the associated production of a Z boson and a charm quark jet (Z + c), and a comparison to production with a b quark jet (Z + b), in pp collisions at a centre-of-mass energy of 8 TeV are presented. The analysis uses a data sample corresponding to an integrated luminosity of 19.7 fb${}^{-1}$, collected with the CMS detector at the CERN LHC. The Z boson candidates are identified through their decays into pairs of electrons or muons. Jets originating from heavy flavour quarks are identified using semileptonic decays of c or b flavoured hadrons and hadronic decays of charm hadrons. The measurements are performed in the kinematic region with two leptons with $p_{\mathrm{T}}^{\ell }>$ 20 GeV, $|{\eta }^{\ell }|<$ 2.1, 71 $<m_{\ell \ell }<$ 111 GeV, and heavy flavour jets with $p_{\mathrm{T}}^{\mathrm{jet}}>$ 25 GeV and $|{\eta }^{\mathrm{jet}}|<$ 2.5. The Z + c production cross section is measured to be $\sigma (\mathrm{p}\mathrm{p}\to \mathrm{Z}+\mathrm{c}+\mathrm{X})\mathcal{B}(\mathrm{Z}\to {\ell }^{+}{\ell }^{-})=$ 8.8 $\pm$ 0.5 (stat) $\pm$ 0.6 (syst) pb. The ratio of the Z + c and Z + b production cross sections is measured to be $\sigma (\mathrm{p}\mathrm{p}\to \mathrm{Z}+\mathrm{c}+\mathrm{X})/\sigma (\mathrm{p}\mathrm{p}\to \mathrm{Z}+\mathrm{b}+\mathrm{X})=$ 2.0 $\pm$ 0.2 (stat) $\pm$ 0.2 (syst). The Z + c production cross section and the cross section ratio are also measured as a function of the transverse momentum of the Z boson and of the heavy flavour jet. The measurements are compared with theoretical predictions.

Corrected the CERN-EP number. Added the journal reference and the DOI. All the figures and tables can be found at http://cms-results.web.cern.ch/cms-results/public-results/publications/SMP-15-009/ (CMS Public Pages)

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